1. Field of the Invention
The present invention relates to a negative curable composition that is favorable for formation of a color image that is a component of a color filter used in liquid crystal displays, solid-state image sensors and the like, to a color filter formed using the negative curable composition, and to a method of producing the same.
2. Description of the Related Art
A staining method, a printing method, an electrodeposition method and a pigment dispersion method are known as methods of producing a color filter used in liquid crystal displays (LCD) and solid-state image sensors (CCD, CMOS and the like).
Among these methods, the pigment dispersion method is a method of producing a color filter by a photolithographic method using a colored radiation-sensitive composition having a pigment dispersed in various photosensitive compositions, which is advantageous in terms of stability with respect to light, heat and the like as a result of the use of a pigment. Further, as a result of patterning by a photolithographic method, positional precision is high, and this method is widely used as a favorable method for producing a color filter for use in a large-screen high-definition color display.
When producing a color filter by the pigment dispersion method, a radiation-sensitive composition is applied onto a glass substrate using a spin coater, a roll coater or the like and dried to form a coating film, colored image pixels are formed by pattern exposure and development of the coating film, and a color filter can be obtained by repeating this operation for respective colors.
A method using a negative photosensitive composition that includes a photopolymerizable monomer and a photopolymerization initiator in combination in an alkali-soluble resin has been disclosed as one of the aforementioned pigment dispersion method (see, for example, Japanese Patent Application Laid-Open (JP-A) Nos. 2-199403 and 2-273411).
In recent years, ever higher definition is demanded of color filters for solid-state image sensors. However, it is difficult to further improve resolution in a conventional pigment dispersion method, and problems occur such as color irregularities caused by coarse pigment particles. As a result of this, this method has not been appropriate for applications requiring a fine pattern such as solid-state image sensors.
In order to address such problems, a technique using a dye instead of the conventional pigment has been proposed (see, for example, JP-A No. 6-75375). Generally, curable compositions including a dye have been inferior compared to curable compositions using a pigment in terms of a number of properties such as light resistance, heat resistance, solubility and coating uniformity. In particular, since a film thickness of 1.5 μm or less is required in the case of producing color filters for solid-state image sensors, a large amount of coloring must be added to the curable composition which can result in insufficient adhesion to a substrate, insufficient curing, insufficient dye even in the exposed portion and other problems that make pattern formation extremely difficult.
Further, ene-thiol polymerization systems have been researched for many years as methods of improving the curability of a curable composition (see, for example, JP-A Nos. 54-63903, 10-253815, 10-253816 and 2006-71890, and Japanese Patent (JP) No. 3120547).
However, in the polymerization system taught in JP-A No. 54-63903, active olefin or aryl ether is used as a compound having an ene structure, which results in problems such as poor stability of the curable composition, and particularly results in a large number of problems in application to formation of a fine pattern.
Further, in the polymerization systems taught in JP-A Nos. 10-253815, 10-253816 and 2006-71890 and JP No. 3120547, a number of applications for thiol compounds in color filter systems are disclosed; however, the type of photopolymerization initiators are limited and the compositions have a specialized system and thus can hardly be said to be versatile techniques. In addition, these references do not teach any findings related to technical disclosure for the formation of fine patterns.
In other words, in conventional techniques related to ene-thiol systems, it has been difficult to form rectangular patterns. In addition, the storage stability of curable compositions has been poor and improvement thereof is required.
The present inventors intensively researched the components of negative curable compositions in order to solve the above problems, as a result of which it was found that a negative curable composition having excellent developability at high sensitivity, and also the capability to form a rectangular fine pattern, could be obtained by using a monofunctional thiol compound in a low-binder content formulation, and thus accomplished the present invention.